The long-term objective of this application is to understand the role of airway smooth muscle in airway hyperreactivity. The proposal will examine the hypothesis that immunizatio can induce changes in airway smooth muscle cell membranes long before there is a release of mediators and an anaphylactic bronchoconstrictive response. The properties of sensitized airway smooth muscle cells will be examined in detail by determining the resting membrane potential and passive membrane characteristics using a microelectrode technique and Abe-Tomita chamber. Membrane permeability to sodium, potassium, calcium, and chloride ions will be determined. Using (14C)-amiloride binding, the density and affinity of sodium entry sites on airway smooth muscle cells before and after sensitization will be quantified. Using purified reaginic antibodies (IgE, IgG) and purified anaphylatoxin (C5a), in concert with immunoflurorescent technique and autoradiography, the presence of Fc and peptide (C5a) receptors on airway smooth muscle cell membranes will be established. Secondly, factors hich may influence the change in membrane properties and/or the binding of specific antibodies to the membranes will be identified. The factors to be examined will include age, temperature, different ion concentrations and pH. In all experiments, the possible involvement of specific mediators of anaphylaxis will be elucidated using specific blocking agents. Additionally, relationship between hyperpolarization and increased airway smooth muscle contractility to histamine and acetylcholine will be studied. The dependence of membrane events (depolarization and hyperpolarization) on the availability of calcium, Na/Ca exchange and sodium influx will be established. Sodium flux in vivo will be manipulated by treating animals with sodium channel inhibitors such as amiloride, ATPase inhibitors such as ovabain or by feeding animals during sensitization a sodium free diet. The ability of these manipulations to attenuate changes in pulmonary function after the inhalation of antigen in vivo will be established. The proposal offers several new concepts pertinent to the understanding of the physiological mechanisms of bronchial asthma.